This invention relates to phased-array scanned antennas, and more particularly to techniques for stabilizing the beam as the frequency is varied.
It is common practice to design radar waveforms with varying frequency when attempting to measure parameters such as target range. Using an extended RF bandwidth offers enhanced measurement resolution of the range parameter. An example of such an extended RF-bandwidth is that used in the formation of a Synthetic Aperture Radar (SAR) map, where the frequency, which varies linearly within the transmitted pulse, can change by up to 5% or more of the center frequency. FIG. 1 shows an exemplary plot of the frequency of a transmitted pulse as a function of time. This is also known as a xe2x80x9cchirpedxe2x80x9d pulse waveform.
As the frequency changes during a pulse, the direction of beam pointing will also change. Hence, a problem to which this invention is addressed is that of beam stabilization for a system employing a frequency-varying waveform such as a chirped pulse waveform.
Known beam stabilization techniques have used spinning analog phase shifters or time delay units. The spinning phase shifters are expensive, heavy, slow to reprogram for new beam pointing positions, and are of limited power handling capability. The time delay units are expensive, bulky, heavy, and suffer from grating lobe formation.
A method is described for maintaining beam pointing (also known as stabilizing) for an Electronically Scanned Antenna (ESA) as its frequency is varied over a wide frequency bandwidth. The technique uses discrete phase shifters, a number of stored states, and a control methodology for rapidly switching among the states, e.g. within a pulse.